Process for the production of hydro-fluoroaromatic compounds



United States Patent 3,270,070 PROCESS FOR THE PRODUCTION OF HYDRO- FLUOROAROMATIC COMPOUNDS Robert N. Haszeldine, Disley, and John M. Birchall, Manchester, England, assignors to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania No Drawing. Original application Apr. 5, 1962, Ser. No. 185,221. Divided and this application Sept. 1, 1964, Ser. No. 399,126 Claims priority, application Great Britain, Apr. 19, 1961, 14,200/ 61 Claims. (Cl. 260650) This application is a division of application Serial No. 185,221, filed April 5, 1962.

This invention concerns a novel reaction between highly fluorinated aromatic compounds and chlorosilanes to provide novel fluoroaro'matic substituted silanes. The invention also concerns novel derivatives of such fluoroaromatic substituted silanes and improved methods of preparing polyfluoroaromatic compounds.

The reaction of chlorosilanes with fluoroolefins is known; for example, tetrafluoroethylene reacts with trichlorosilane to form an addition product of the formula SiCl CF CF H. The reaction of chlorosilanes with highly fluorinated aromatic compounds might be expected to follow a similar course resulting in an addition product, but it has been surprisingly found that the reaction follows a completely different course. Instead of an addition product, a substitution product is formed in which a fluorine atom is eliminated from the aromatic ring and a chlorine atom on the silicon atom is replaced by fluorine.

The reaction may be written as follows:

where Ar is a highly fluorinated aryl radical, R is hydrogen, alkyl, aryl, fluoroalkyl, fluoroaryl, or fluorine, and n is zero or an integer of 1 or 2. When, in the above formulae, n is 2 the R substituents may be the same or different.

The fluoroaryl radical Ar; will preferably be a perfluoroaryl radical. Also included in this invention are fluoroheterocyclic radicals having aromatic characteristics. The preferred Ar, radicals are perfluoroaryl radicals such as perfluorophenyl and perfluoronaphthyl radicals. The Ar radicals may be substituted with alkyl or perfluoroalkyl groups; e.g. methyl, perfluoromethyl, ethyl, isopropyl, n-butyl, t-butyl, perfluoroethyl, etc. Thus, examples of specific perfluoroaryl radicals will include perfluorophenyl, perfluorotolyl, perfluoronaphthyl, perfluoro (methylnaphthyl) perfluoroxylyl, perfiuoro (ethylphenyl) 2,3,4,5-tetrafluorotolyl, 2,3,5,6-tetrafluorotolyl, 2,3,4,5,6, 7-hexafluoronaphthyl, 2,3,4,S-tetrafluorophenylethyl, 2,3, S-trifiuor-o-4-methylpyridyl and the like. In general the fluoroaryl radical will be any of the defined highly fluorinated aryl radicals which contain from 6 to 12 carbon atoms. The R radicals defined above will preferably be hydrogen, fluorine, lower alkyl and fluoroalkyl radicals (e.g.) methyl, ethyl, propyl, butyl) perfluoromethyl, etc. and aryl and fluoroaryl radicals containing six to ten carbon atoms (e.g. phenyl, perfluorophenyl, perfluorotolyl, ethylphenyl, naphthyl, etc.

More specifically, when the reactants are hexafluorobenzene and trichlorosilane the reaction is as follows:

The surprising features of the reaction are (a) that it ice is the first reported instance of free radical attack upon a highly fluorinated aromatic system to give an aromatic product and (b) that in the course of the reaction a fluorine atom migrates from the aromatic nucleus to the silicon atom.

The reaction is favored by conditions conducive to the formation of free radicals, particularly irradiation by ultraviolet light and/or heat. Chemical initiators may be used as well as or instead of such external activation energy sources. The chemical initiators used may be of any of those usually used in initiating free radical reactions including organic peroxides such as benzoyl peroxide and azo-compounds such as dimethyl-azo-diisobutyrate. When using actinic radiation as the initiating agent heat is not essential and the reaction may be conveniently conducted at room temperature or lower. With chemical initiators, however, heat will usually be required and temperatures of from 50 to 500 C. are found satisfactory.

As indicated by the formula given, the product of the reaction is mainly a mono-substituted aromatic compound. This is particularly so when a molar excess of the fiuoroaromatic compound is used. However, when substantially equimolar quantities, or a major excess of the silane are used, some higher substitution products are obtained, e.g.

The reaction is generally applicable to all highly fluorinated aromatic compounds, including highly fluorinated compounds containing a heterocyclic ring having aromatic characteristics such as perfiuoropyridine. For the avoidance of doubt, it is here stated that the definition of Ar as defined above, is intended to include radicals derived by the removal of a fluorine atom from the aromatic ring of such highly fluorinated compounds. The heterocyclic Ar radicals will be derived from heterocyclic compounds such as and the like. Particularly preferred perfluoroaromatic compounds are those of the formula C F (R where R is perfluoroalkyl and m is an integer of from 1-6.

The preferred mono-substituted products of the invention form a new class of aromatic substituted silanes of the formula Ar SiFCl R,,, where Ar R, and n are as defined above. Particularly preferred products are those of the formula Ar SiR'FX where R is hydrogen, alkyl, aryl, fluoroalkyl 0r fluoroaryl, and X is chlorine or fluorine, the alkyl, aryl, fluoroalkyl and fluoroaryl radicals containing from one to ten carbon atoms. The silane products of this latter formula are readily hydrolyzable by water to form a series of novel silicones and polysiloxanes which are stable thermally and particularly stable to water and acids. In strong aqueous alkali further hydrolysis of the silicones and polysiloxanes takes place in the course of which the silicon atom on the perfluoroaromatic nucleus is replaced by hydrogen. This is a particularly useful reaction since once a hydrogen is introduced into a perfluoroaromatic system it provides a point for further chemical attack thereby enabling conversion into other useful chemicals.

The novel silicones which may be prepared according to this invention from the mono-substituted derivatives are of the general formula (Ar SiRO) where Ar and R are as previously defined and z is an integer. They may be prepared by reacting the fluoroaromatic compound with a silane of the formula R'SiHClX followed by hydrolysis of the silane formed with water, e.g.

U.V. light CaFa RSiHClX Where the starting silane is dichlorosilane there arises the possibility of a two stage reaction with the fluoroaromatic compound, for example:

V. light & CeFc The novel siloxanes which may be prepared according to this invention from the mono-substituted derivatives are of the general formula (Ar SiO Where Ar and z are as previously defined. They may be prepared by-the reaction of the fluoroaromatic starting compound with a silane of the formula SiHClXY where X and Y are fluorine or chlorine, followed by hydrolysis with water, for example:

U.V.llgl1t 11,0

CsF l-SiHClg CrFssiFC z '(CuF5 iO1.a)1

Where hydrolysis is carried out on a silane of structure Ar SiR F where R is alkyl, aryl, fiuoroalkyl or fluoroaryl, the products obtained are disiloxanes, viz.:

As stated above the novel silicones and polysiloxanes are highly stable except to strong alkali in which they are further hydrolyzed, for example:

' NaOHaq. 035 0191 CGFH There is of course no need to proceed via a silicone or polysiloxane to obtain the hydrogen containing perfluoroaromatic derivative, since the silane products, including those containing only one halogen atom attached to the silicon atom may be hydrolyzed directly by strong alkali, e.g.

NaOHaq. C5F5SiFCl2 CQF5H It will be seen therefore that the invention provides a route to inonohydroperlluoroaromatic compounds which is especially useful for preparing compounds of the type C F H(R where m is 1-6. Particularly the invention provides a new route to pentafluorobenzene and the best method yet produced for the conversion of hexafiuorobenzene into pentafluorobenzene. From penta fluorobenzene and other monohydroperfluoroaromatic compounds other useful intermediates may be prepared such as C F I and C F Br.

The higher substituted silane products, which may, as indicated, be obtained by the reaction of the perfluoroaromatic compound with an equimolar or a molar excess of the silane, with or without the separation of a lower substituted intermediate, are also subject to hydrolysis in a similar manner to the mono-substituted products. Of particular note are the polyhydroperfluoroaromatic compounds which are formed by hydrolysis in strong aqueous alkali, e.g.

Besides being useful intermediates, the thermal and chemical stability under neutral and acid conditions of the silicones and siloxanes renders them useful as lubricant oils and greases and resins.

The invention is illustrated by the following examples:

EXAMPLE 1 (a) Preparation of (penlafluorophenyl)dichlorofluorosilane Dry hexafluorobenzene (10.0 g., 0.054 mole) and freshly distilled trichlorosilane (8.0 g., 0.059 mole) were sealed into a 350 ml. silica tube and irradiated by a 500 watt mercury discharge tube for 250 hours. The reaction tube was shaken vigorously throughout this period. At the end of the irradiation, the tube was cooled to C., and volatile products (790 ml. at N.T.P.; M.W. 38.9) were transferred to a high-vacuum apparatus and identified by infrared spectroscopy as hydrogen chloride containing traces of silicon tetrafiuoride. The liquid reaction products were transferred and distilled under dry nitrogen and yielded fractions boiling 80 148 C. (1.8 g.) and 148170 C. (6.2 g.). The latter fraction was redistilled under reduced pressure and gave (pentafiuorophenyl)dichlorofiuorosilane (5.0 g.). (Found: C, 25.2, CI. 25.1, F, 38.9%. C CI F Si requires: C, 25.3, Cl, 24.9, F, 40.0%), B.P. 54 C./13 mm. Gas-liquid chromatographic analysis of the remaining fractions from the distillations showed that some hexafiuoro'benzene (2.2 g., 22%) remained unreacted, and analysis of the silicon-containing fractions by bydrolysis showed that the total yield of (pentafluorophenyl)dichlorofiuorosilane was at least 7.2 g. (60% based on hexafluorobenzene transformed).

(b) Hydrolysis of (pentafluorophenyl)dichlorofluorosilane Water (25 ml.) was added in five portions to (pentafluorophenyl)dichlorofluorosilane (24.0 g.) contained in a partially evacuated 2.5 liter bulb; a vigorous reaction occurred at each addition and a white polysiloxane was formed. Aqueous sodium hydroxide (40%; ml.) was then added slowly and the reaction was completed by heating on a steam bath for 15 minutes. The volatile contents of the bulb were transferred to a high-vacuum apparatus, dried with phosphorus pentoxide, and identified as pentafluorobenzene (10.0 g., 71%) by elemental analysis and molecular weight measurement. (Found: C, 42.8%; H, 0.9%; M, 168. Calc. for C HF C, 42.8; H, 0.6%; M, 168.) The purity of this product was confirmed by gas-liquid chromatography.

EXAMPLE 2 Reaction of 2,3,4,5,6-pentafluorotoluene with trichlorosilane 2,3,4,5,6-pentafluorotoluene (18.4 g., 0.10 mole) and trichlorosilane (14.8 g., 0.11 mole), in a 350 ml. sealed silica tube, were irradiated by a 500 watt mercury discharge lamp for 192 hours. The gaseous products (1331 m1. at N.T.P. Found: M 44) were shown by infrared spectroscopy to consist of hydrogen chloride, silicon tetrafluoride, and a trace of carbon dioxide. The liquid products were distilled and gave 2,3,4,5,6-pentafluorotoluene (9 g.), B.P. 116-120 C., and a fraction B.P. 92-99 C./37 mm. (7 g.). The latter was redistilled to give a liquid (5.6 g., 39% based on pentafiuorotoluene converted), B.P. 98-99 C./37 mm., which was shown to consist of a mixture of isomeric (methyltetrafluorophenyl)dichlorofluorosilanes by elemental analysis, (Found: C, 29.8; H, 1.1. C7H3C12F5Si requires: C, 29.8; H, 1.1%), and gas-liquid chromatography. The infrared spectrum of this product was consistent with the proposed structure.

By following the procedural details given in the 8.12

examples, the following reactions may be carried out to obtain the products indicated: An SiHClauRn Product An SiHC lnRu Product and isomers CHzCHaCHs CH2CH2CI-I3 F3 (F F:

F F SiHCliCeI-h F SiFClCuHs F F SiI-IClzCH3 F SiFClCH F F F r F F F F F F F F and isomers and meta and para isomers SiF(CIIa)2 F F F F F F F b F F SiHOl2F F SiF Cl H3C SiI-ICMCHm. F \CH3 F F F F F F F VF F F F F F F F F and lpha isomer and isomers F F u i q F F SH 01 F F Llkewlse when the caustic hydrolysis step of Example 2 Z 1 is carried out, products are obtained as follows:

F F F Si FHCl N N 0 Compound Hydrolyzed Product Obtained and meta and para isomers F F F F 0 F3 C Fa F SiFzCl F H F F SiHOI C H U F SiFClCaHs F F F F F F F 0 Fa F 0 F3 F F F F F F F F F and isomers F F F SiFHCl F H F F SiHClflO6H5 F SiFCICflHs N N CFa CF: F F F F I F F F SlFClC6I 5 F H C F; C Fs C F3 l CFa- F CF3 F F F SiHzCh F S'i F F F F F F F F F F If instead of using strong alkaline hydrolysis, simple F F F aqueous hydrolysis is employed, silicones and siloxanes F F may be obtained as follows:

F F SIHCMCHB) F slFwHm Compound Hydrolyzed Product Obtained F F F F rcmnsim [(CtF5)2SiO]z F 1? (CFa-CaFOrSlFp Fr-CsF-Qr SlOh CF C F4SiFC12 (CF3CnF4 r.5)z F F F F r 0 F F SiI-ICl(CHa)2 F siFwHm It will be Obvious to the skllled art worker that numerou changes and variations may be made from the above de- F\ F F F scription of the invention and the examples Without de- F N F N parting from its spirit and scope.

. We claim: andlsomers 1. A process for the preparation of a monohydroper- F F fiuoroaromatic compound when x is 1 or a dihydroper- F N SiHChFnm N F fluoro aromatic compound when x is 2, x being defined below, which comprises hydrolyzing with the aid of strong F F F S1F2C1 alkali in admixture with water a compound having the N N structure Ar (SiFCl R where Ar is a perfluoroaryl radical selected from the group consisting of perandimmers fiuorophenyl, perfluoronaphthyl and perfluoropyridyl, 31: CF3 R is a radical selected from the group of hydrogen, fluorine, alkyl, aryl, fluoroalkyl and fluoroaryl F F SiH Cl F s1 FHCl radicals, n is a number from O to 2, and x 18 a number from 1 to 2. F F F F 2. A process for the preparation of monohydroperl fluoroaromatic compounds which comprises hydrolyzing CH3 CH3 with the aid of caustic in admixture with water a compound of structure Ar SiR'FX where Ar is perfluoroaryl radical selected from the group consisting of perfiuorophenyl, perfluoronaphthyl and perfluoropyridyl, R is a member selected from the group of hydrogen, alkyl, aryl, fluoroalkyl and fluoroaryl radicals, and X is a member selected from the group of fluorine and chlorine atoms.

3. A process for the preparation of a monohydrofiuoroaromatic compound which comprises hydrolyzing with the aid of strong alkali in admixture with water a compound having the structure Ar (SiFC1 R where Ar is a pe'rfluoroaryl radical selected from the group consisting of perfluorophenyl, perfiuoronaphthyl and perfluoropyridyl, R is a radical selected from the group consisting of hydrogen, fluorine, alkyl, aryl, fluoroalkyl and fluoroaryl radicals and n is a number from 0 to 2.

4. A process for preparing a monohydroperfluoroaromatic compound which comprises hydrolyzing with aqueous sodium hydroxide a com-pound having the structure Ar SiFCl R. Where Ar is a perfluoroaryl radical selected from the group consisting of perfluorophenyl, perfluoronaphthyl and perfluoropyridyl, n is a number from 0 to 2, and R is fluorine.

5. A process for the preparation of pentafiuorobenzene which comprises hydrolyzing (pentafluorophenyl)dichlorofluorosilane with aqueous caustic.

References Cited by the Examiner UNITED STATES PATENTS 2,511,820 5/1950 Barry et a1 260448.2 2,598,436 5/1952 Mohler et a1. 260448.2 2,636,896 4/1953 Frost 260448.2 2,929,830 3/1960 Kunowski 260448.2 3,000,976 9/1961 Patrick et a1. 260650 3,004,077 10/1961 Banks et al 260-650 FOREIGN PATENTS 534,818 12/1956 Canada. 1,205,608 2/ 1960 France.

706,703 4/1954 Great Britain.

LEON ZITVER, Primary Examiner.

K. V. ROCKEY, Assistant Examiner. 

1. A PROCESS FOR THE PREPARATION OF A MONOHYDROPERFLUOROAROMATIC COMPOUND WHEN X IS 1 OR A DIHYDROPERFLUORO AROMATIC COMPOUND WHEN X IS 2, X BEING DEFINED BELOW, WHICH COMPRISES HYDROLYZING WITH THE AID OF STRONG ALKALI IN ADMIXTURE WITH WATER A COMPOUND HAVING THE STRUCTURE ARF(SIFCL2-NRN)X WHERE ARF IS A PERFLUOROARYL RADICAL SELECED FROM THE GROUP CONSISTING OF PERFLUOROPHENYL, PERFLUORONAPHTHYL AND PERFLUOROPYRIDYL, R IS A RADICAL SELECTED FROM THE GROUP OF HYDROGEN, FLUORINE, ALKYL, ARYL, FLUOROALKYL AND FLYOROARYL RADICALS, N IS A NUMBER FROM 0 TO 2, AND X IS A NUMBER FROM 1 TO
 2. 